Enhancing timing of Ce-doped garnet scintillators by complex codoping

The work deals with timing characteristics of garnet scintillation materials, especially for applications like time-of-flight PET or future collider experiments. While cerium-activated oxide scintillation single crystals are known for their fast performance due to rapid d-f relaxation in Ce³⁺. Meanwhile, the extended scintillation decay time of Gd3(Al,Ga)5O12:Ce (GAGG:Ce), the brightest oxide scintillator, still does not meet the requirements for the upgrade 2 of the central part of the LHCb electromagnetic calorimeter in CERN. Additionally, GAGG:Ce and other Ga-containing scintillators are typically grown in large sizes exclusively in Ir crucibles. Attempts to substitute Ga with Sc in the gadolinium garnet Gd3(Al,Sc)5O12:Ce (GSAG:Sc,Ce) grown from Mo crucibles resulted in a significant decrease in light yield compared to GAGG:Ce, although without a notable improvement in timing.The results obtained in this work certify that tuning the doping concentrations of Ca2+ and Mg2+ ions provides the enhancement of timing performance of Ce-doped YAG and GAGG scintillators due to elimination of carrier traps and acceleration of carrier transport to luminescence centers, independently on the host composition. Apart of that, YAG is more promising as host, because it can be obtained in cheap W/Mo crucibles in contrast to GAGG and other Ga-containing crystals. Due to the synergy between Ca2+ and Mg2+ dopants in garnets hosts, we demonstrated that improved combination of light yield and decay time can be achieved in Ce-doped garnets, i.e. larger number of prompt photons can be generated for fast-timing applications. At the same time, Sc,Ca codoped YAG:Ce is another promising approach to get fast scintillation crystals with a high light yield that may be grown by a cheap technology from W crucibles.